1. Technical Field
The present invention relates to a semiconductor device, and more particularly, to a method for manufacturing a semiconductor device, in which a plurality of bottom antireflective coating films are deposited to prevent a standing wave caused by a light source having a short wavelength used in forming a fine pattern.
2. Discussion of the Related Art
Previously, for an exposure process using a light source in the mid ultra violet (MUV) region of the spectrum, only a photoresist film was coated on a wafer before an exposure process.
Recently, a light source such as KrF in a deep ultra violet (DUV) region of the spectrum is used to form a fine pattern on a′ wafer. In this case, a bottom anti reflective coating (BARC) film is formed below the photoresist film to solve a problem generated when light enters the wafer below the photoresist film. In case of a DUV having a short wavelength, the DUV is reflected on the wafer through the photoresist film and causes interference with incident light source. For this reason, a standing wave occurs, which impedes the formation of a photoresist film having a uniform profile. That is, the bottom antireflective coating film serves to prevent the light, which has passed through the photoresist film, from being reflected externally.
Hereinafter, a related art method for manufacturing a semiconductor device will be described with reference to the accompanying drawings.
FIG. 1 is a scanning electron microscope (SEM) view illustrating the variation of a photoresist film after exposing the photoresist film on a wafer having no bottom antireflective coating film, and FIG. 2 is a scanning electron microscope (SEM) view illustrating the variation of a photoresist film after exposing the photoresist film on a wafer having a bottom antireflective coating film.
As shown in FIG. 1, in case where no bottom antireflective coating film is formed below a photoresist film, external incident light enters a wafer and is reflected therein. The reflected light interferes with another incident light to cause a standing wave. Therefore, as shown in FIG. 1, the standing wave interferes with the formation of a uniform profile of the photoresist film formed by exposure and developing processes.
Referring now to FIG. 2, a bottom antireflective coating film is formed below the photoresist film so as not to externally reflect the incident light. Thus, a standing wave is avoided. Unlike FIG. 1, it is noted from FIG. 2 that a uniform profile of the photoresist film is formed.
If a bottom antireflective coating film is used, loss of the photoresist film occurs when the bottom antireflective coating film is etched. Considering this loss, the photoresist film should be formed to have a greater thickness. In this case, although the standing wave is avoided, the thicker photoresist film causes other problems.
As shown in FIG. 1, if a standing wave occurs, variation in the critical dimension (CD) may be caused depending on the height or thickness of the photoresist film. If an MUV light source is used to form a pattern having a large design rule (large CD), a variation of CD caused by the standing wave is not a serious problem. However, if a KrF-based light source is used to form a pattern having a small design rule, variation of CD caused by the standing wave may create a serious problem. Therefore, in the exposure process using KrF as a light source, the bottom antireflective coating film is formed below the photoresist film to prevent the standing wave from occurring.
Meanwhile, the bottom antireflective coating film absorbs the light source, which has passed through the photoresist film, to prevent a standing wave from occurring. However, absorbency of the light source by the bottom antireflective coating film depends on the thickness of the bottom antireflective coating film and the types of material layers below the bottom antireflective coating film.
FIG. 3 is a graph illustrating reflexibility of the bottom antireflective coating film depending on its thickness varied per bottom material layers.
Referring to FIG. 3, ‘a,’ ‘b’ and ‘c’ show that different sub-material layers exist below the bottom antireflective coating film.
As shown in FIG. 3, it is noted that the bottom antireflective coating film has minimum reflexibility at a specified thickness. That is, it is noted from the cases ‘a,’ ‘b’ and ‘c’ that reflexibility is varied depending on the material layers below the bottom antireflective coating film.
Therefore, the thickness of the same bottom antireflective coating film is varied depending on the material layers. The thickness of the bottom antireflective coating film will easily be determined if the case ‘a’ of FIG. 3 is only considered. That is, in ‘a’ of FIG. 3, the bottom antireflective coating film may be formed at a thickness of about 580 nm showing the lowest reflexibility. However, in this case, the cases ‘b’ and ‘c’ are not considered. The case ‘c’ substantially shows low reflexibility but the case ‘b’ shows serious reflexibility of 0.2. Therefore, in cases where different material layers are deposited below the bottom antireflective coating film, it is difficult to select the thickness of the bottom antireflective coating film suitable for a proper antireflective effect.
Furthermore, it is noted that a bottom antireflective coating film having a thickness of about 850 nm or greater is required to obtain low reflexibility for all the material layers below the bottom antireflective coating film. However, in this case, another problem may arise in that planarization is not uniform.
The aforementioned method for forming a fine pattern has the following problems.
First, reflexibility of the bottom antireflective coating film is varied depending on types of the bottom material layers. Therefore, if different material layers exist below the bottom antireflective coating film, it is difficult to form the bottom antireflective coating film that meets low reflexibility for all the material layers.
Second, when different material layers exist below the bottom antireflective coating film, the bottom antireflective coating film should be thickly formed to obtain low reflexibility. If the bottom antireflective coating film formed by spin coating is formed to be thick, a problem occurs in that poor planarization may result. If planarization is not good, further problems may occur in later processes such as exposure, developing and etching processes.